1. Field of the Invention
This invention relates to a binderless zeolite molding, a method for the production thereof, and uses thereof.
2. Description of the Related Art
The ZSM-5 type zeolite designates crystalline metallosilicates represented by crystalline aluminosilicates which have the pores of 10 oxygen atom-membered ring as disclosed in U.S. Pat. No. 3,702,886. As regards the crystalline aluminosilicates which have silicon and aluminum as metallic components of the crystal skeleton of zeolite, the practice of preparing or using crystalline metallosilicates in which the Al3+cation being substituted with another metal ion for the purpose of controlling mainly the acidic quality thereof has been widely in vogue. Silicalite without aluminum having the same structure as the above or the crystalline metallosilicates in which the aluminum being substituted with another metal ions are generally called the ZSM-5 type zeolite (the MFI type according to the Framework Topology Code adopted by International Zeolite Association).
As a method of synthesizing the ZSM-5 type zeolite, the hydrothermal synthetic method has been known in which a water slurry using tetra-n-propylammonium ion as a template agent is adopted as the raw material for the zeolite.
In the conventional hydrothermal synthetic method, however, the raw material components are partly dissolved in water while they are being heated. The proportion of the components to be converted into crystals, therefore, is inevitably decreased and the time for the crystallization is elongated greatly because the alkaline component is diluted. By the method of such slow crystallization, crystals of large sizes are liable to grow and, moreover, different metal ions from silicon are liable to be expelled from the crystal lattice. The atomic ratio of Si/Al in the water slurry, therefore, does not always coincide with the atomic ratio of Si/Al of the produced ZSM-5 type zeolite. Further, this method performed on a commercial scale entails the following problems, because it requires the water slurry to be heated, that it necessitates a closed, large reaction vessel proportionately to the weight of the resultant crystal, requires an expensive, much template agent, emits an effluent in a large volume and the process for filtering and calcining zeolite powder is complicated.
In the production of a molding of conventional zeolite, the zeolite used solely manifests poor formability. This production, therefore, requires first to synthesize zeolite powder by the hydrothermal synthetic method and thereafter form the powder in shape by utilizing an inorganic binder. This method is required to choose a binder which is incapable of exerting any adverse effect on the intended use of the product. It further requires the inorganic binder in a large amount for enabling the product to acquire fully satisfactory strength. This production, therefore, is at a disadvantage in not only lowering the zeolite content in the produced molding but also disabling effective utilization of zeolite buried in the binder.
In the circumstances, methods for producing moldings of zeolite substantially without binders have been proposed. For example, several moldings of crystalline type binderless aluminosilicates are taught in JP-A-59-162,952 (TSZ type aluminosilicates), JP-A-61-72,620 (MOR type aluminosilicates), and JP-A-62-138,320 (FAU type aluminosilicates) have been known. In these methods, formed masses are produced by preparing, as the secondary raw material, a synthesized zeolite powder in advance and treating the zeolite powder with a clayey mineral or an inorganic binder such as silica-alumina. Since their binders in the formed masses are converted into zeolites by treating the masses with an alkali solution, they require hydrothermal synthesis substantially twice. They, therefore, entail such problems as elongating the process and enlarging the amount of effluent. Further, these methods require the atomic ratio of Si/Al in the aluminosilicate as the secondary raw material to coincide with the atomic ratio of Si/Al in the inorganic binder. Incidentally, since the formability of the aluminosilicate is degraded when the inorganic binder has a small aluminum content, the production of a molding of a binderless aluminosilicate having a large silica content or the production of a binderless zeolite with a crystalline metallosilicate substantially without aluminum has never been attained. The crystallization is attained by performing the process of hydrothermal synthesis twice. It has, therefore, entailed such problems as encountering difficulty in taking the aluminum into the zeolite lattice and inevitably forming impurities in the product from the aluminum outside the lattice.
As described above, the molding of a ZSM-5 type binderless zeolite in which substantially no aluminum is present outside the crystal lattice has never been known to the art.
A method for producing a supported type molding of zeolite by utilizing an inorganic carrier has been also proposed. For example, JP-A-11-165,074 teaches a method which includes supporting a hydrogel composed of tetraethyl orthosilicate, tetraethyl orthotitanate, and tetrapropylammonium hydroxide on a silicon oxide carrier and thereafter treating the supported hydrogel with steam under pressure thereby producing the MFI type crystalline titanosilicate on the carrier. According to this method, the amount of the hydrogel to be supported on the carrier is extremely small because the hydrogel has such a low concentration as to acquire flowability enough for support of the hydrogel on the carrier. The supported type molding of zeolite which is obtained by this method entails the problem of having an extremely low zeolite content.
The beta type zeolite (the BEA type according to the Framework Topology Code adopted by International Zeolite Association) designates the crystalline metallosilicates represented by the crystalline aluminosilicates which have the pores of 12 oxygen-membered ring as disclosed in U.S. Pat. No. 3,308,069.
The moldings of beta type zeolite entail the same problems as the ZSM-5 type zeolite mentioned above. The molding of a binderless zeolite which contains substantially no binder has never been known to the art.
The MEL type zeolite designates crystalline metallosilicates as disclosed in U.S. Pat. No. 3,709,979. The MEL type zeolite is a tetragonal zeolite. The two kinds of intersecting pores which are formed of a 10 oxygen-membered ring are both straight. The openings of these pores are identical ellipses.
Heretofore, the method of hydrothermal reaction has been known as a way of synthesizing the MEL type crystalline metallosilicate. This method uses, as the raw material, a water slurry utilizing tetra-n-butylammonium ion as a template agent. JP-B-05-323,280, for example, teaches a method which includes preparing a water slurry having a SiO2 concentration of about 10 wt. % and permitting uniform mixture by agitation and causing this water slurry to react under hydrothermal conditions (100xc2x0 C., autogenous pressure) for 23 days thereby effecting crystallization of the MEL type crystalline metallosilicate.
The molding of the MEL type zeolite entails the same problems as the ZSM-5 type zeolite mentioned above. That is, the molding of a binderless zeolite which contains substantially no binder has not been known to the art.
This invention has been initiated in view of the above problems entailed by the prior art. It is an object of this invention to provide a method for producing a molding of zeolite without inorganic binders.
Another object of this invention is to provide a molding of binderless zeolite.
Yet another object of this invention is to provide use for the molding of binderless zeolite.
This invention concerns a method for producing a molding of binderless zeolite, characterized by exposing to saturated steam a zeolite precursor represented by the formula (1):
Si(SDA) xMyQzxe2x80x83xe2x80x83(1)
wherein SDA denotes a tetraalkylammonium, M an alkali metal, Q a metal element incorporated in the crystal skeleton of zeolite (except for silicon), x a numeral in the range of 0.001 to 1, y a numeral in the range of 0.0001 to 1, and z a numeral in the range of 0 to 0.5.
This invention concerns a molding of binderless zeolite, characterized by the fact that the zeolite has at least one crystal structure selected from the group consisting of MFI type MEL type, BEA type, and the intergrowth of MFI type and MEL type.
This invention further concerns use of the molding of the binderless zeolite mentioned above as a catalyst for the production of an alkanolamine.
The above and other objects, features and advantages of the present invention will become clear from the following description of the preferred embodiments.